Ear-canal based acoustic measurements known as wideband acoustic immittance (WAI) tests are showing promise as powerful middle-ear assessment tools, with potential for significant advantages over traditional middle-ear assessment measures. Some advantages of WAI include the ability to obtain responses over frequencies important for speech perception (0.25-8 kHz), heightened sensitivity to age-related changes in the acoustic properties of the middle ear, improved sensitivity to a wide variety of middle-ear disorders, and the ability to predict conductive hearing loss (CHL). Furthermore, because medical management decisions (i.e., antibiotics and/or surgery) with some middle-ear disorders are often based on the presence/absence of a conductive hearing loss (CHL), the ability to rely on an accurate, objective middle-ear tests to detect CHL may help restrict the unnecessary use of surgery and/or antibiotics. While identification of maturational effects on WAI for some age groups has brought to light the need to develop age-specific normative data, absence of sufficient study of age-related differences in WAI across a broad age range and a comprehensive normative database severely limits the clinical application of WAI tests. Therefore, the aims of this proposal are to gather WAI data from individuals across a broad age range (6 months to 75 years) to, 1) identify age-related differences in WAI characteristics and build a WAI normative database across a broad age range, 2) Identify longitudinal changes in WAI data for a subgroup of subjects (6 to 11 months) to track middle-ear development with more samples across a time period when the greatest changes in WAI are expected to occur, and 3) describe the natural history of changes in middle-ear function for ears with otitis media with effusion (OME) to determine if distinctive WAI characteristics emerge during the progression of pathology At the completion of the proposed project, it is our expectation that we will have identified ages at which significant maturational effects on WAI are present, established a comprehensive WAI normative database at selected ages from infancy through adulthood, and obtained valuable results on the natural history of OME in children. Inasmuch as WAI has potential to significantly improve our ability to identify middle-ear dysfunction and predict CHL, having a normative database to provide context with which to interpret WAI measurements from ears with middle-ear disorders will be a significant step forward in enhancing the clinical utility of WAI tests.